The invention relates to a method and circuit arrangement for transmitting data between two time multiplex systems via a common transmission path. Each time multiplex system produces frames which are respectively formed from a prescribed number of binary characters. These frames contain the data and one synchronization word.
In the last few years, time multiplex systems have greatly gained in importance vis-a-vis frequency multiplex systems used until now. Time multiplex systems assign an available bit flow in chronological sequence in a periodically repeating manner to a multiplicity of data channels, respectively. The period of this process is characterized as a frame. Each frame contains a prescribed number of binary characters representing a synchronization word in addition to the data, with the aid of which the data are assigned to the data channels of the time multiplex system.
The bit flow has a prescribed transmission rate or signalling speed of, for example, 2400 bits/sec. If transmission paths are available which permit a greater transmission rate of e.g. 4800 bits/sec., it is desirable to transmit the bit flows of several time multiplex systems via this transmission path. In such a data transmission, the respective binary characters or frames are transmitted via the transmission path in chronological sequence. The binary characters or frames must again be assigned to the respective time multiplex systems at the receiver side.
It would also be possible to provide transmission units, e.g. modems (modulator-demodulators), arranged between the time multiplex systems and the transmission path with one channel divider, respectively, which connects through the binary characters or frames of the first or of the second time multiplex system to the transmission path according to a time multiplex system in chronological sequence or again divides to the respective time multiplex systems at the receiver side. In such a method an assignment can be produced such that additional synchronization words can be transmitted at the beginning of the transmission, for example. With these synchronization words, the assignment of the data subsequently transmitted relative to the time multiplex systems can be determined. However, such a method has the disadvantage that no continuous monitoring of the assignment takes place. Thus, in case of a malfunction it would be possible that the receiver sides of the time multiplex systems respectively receive the data which are assigned to the other time multiplex system, respectively.